Heterocyclic systems. Part 6. Reactions of 4-oxo-4H-[1]benzopyran-3-carbonitriles with hydrazine, phenylhydrazine, hydroxylamine, and some reactive methylene compounds
Hydrazine and phenylhydrazine undergo 1 : 2 addition to the carbonitrile function of 4-oxo-4H-[1]benzopyran-3-carbonitriles (1; X = H, Me, Cl, and Br) to form the iminohydrazine intermediates (2; non-isolable when R = H, and isolable when R = Ph) that further cyclise to yield 3-amino-[1]benzopyrano[4,3-c]pyrazoles (5) and 3-amino-4-(2-hydroxybenzoyl)-1-phenylpyrazoles (7; R = Ph) respectively. Hydroxylamine by similar 1 : 2 addition to the carbonitriles (1) gives 3-[hydroxyamino(imino)methyl]-4-oxo-4H-[1]benzopyrans (9), which undergo no further transformation under acidic conditions. In their reactions with the carbonitriles (1) or 4-oxo-4H-[1]benzopyran-3-carbaldehyde oximes (15), reactive methylene compounds such as acetylacetone, ethyl acetoacetate, diethyl malonate, and ethyl cyanoacetate in the presence of a base undergo Michael addition to the γ-pyrone system with concomitant opening of the pyrone ring and subsequent cyclisation to give benzopyrano[2,3-b]pyridine derivatives, (11), (12), (13), and (14), respectively.